While performing a ligament surgery procedure, it is often necessary for a surgeon to drill one or more tunnels or bores through a patient's bone. In such a ligament surgery procedure, the surgeon typically employs a surgical instrument to drill, in an antegrade fashion, a tunnel through the bone and into a space in the bone joint. Using the same surgical instrument or a different surgical instrument, the surgeon then typically deploys at least one cutter or blade of the surgical instrument within the bone joint space, and actuates the cutter or blade to drill, in a retrograde fashion, a counter bore through the bone along essentially the same path as the tunnel previously drilled in the antegrade fashion. In this way, a recipient socket can be formed in the patient's bone for placement and/or fixation of a tendon graft.
To assure proper formation of the recipient socket in the patient's bone, it is important for the surgeon to drill the counter bore through the bone to a desired depth. One known technique for measuring or otherwise gaging the depth of a tunnel or bore drilled through bone involves the use of a retrograde drill having a retrograde drill pin, and a drill depth grommet disposed on the retrograde drill pin. To obtain the desired depth of the tunnel or bore to be drilled through the bone, the surgeon can read markings on the retrograde drill pin relative to the patient's skin or bone surface before and during the formation of the recipient socket. However, such an approach for measuring or gaging the depth of a tunnel or bore drilled through bone can be difficult for a surgeon to perform, and can frequently produce less than accurate measurement results.